Switching power supply circuit

Abstract

A switching power supply circuit arranged such that stability of each output voltage is enhanced and the device is kept from being large-sized. Secondary winding N2 of transformer T1 is grounded at one end through diode D1: the other end of the secondary winding N2 is connected to first output terminal 2; and tap CT thereof is coupled to second output terminal 3 through diode D2; and capacitors C2 and C3 are connected between the first output terminal 2 and ground and between the second output terminal and ground respectively. In addition to being arranged as above, the present switching power supply circuit is further arranged such that first output voltage V 01L is obtained from feedback voltage generated at the whole of the secondary winding N2, while second output voltage V 02H is obtained from combination of induced voltage generated at winding section n21 defined through division by the tap CT of the secondary winding N2 and the first output voltage V 01L .

What is claimed is: 
     
       1. A switching power supply circuit comprising: a first series circuit of a switching element and a first winding;   a second series circuit of a first rectifying element, a first winding, and a second winding, said series circuit being connected between a reference potential point and a first output terminal, said first rectifying element being connected to said reference potential point;   a first capacitance element connected between said reference potential point and said first output terminal;   a second rectifying element connected between connection point between said second and third windings and a second output terminal;   a second capacitance element connected between said reference potential point and said second output terminal; and   a control circuit for controlling operation of said switching element.   
     
     
       2. A switching power supply circuit according to claim 1, further comprising a transformer including a primary winding constituted by said first winding, wherein the connection point between said second winding and said third winding is adapted to serve as tap provided on a secondary winding of said transformer, and wherein said second winding is constituted by one of winding sections of said secondary winding divided by means of said tap, and said third winding is formed by the other one of said winding sections. 
     
     
       3. A multi-output type switching power supply circuit wherein a plurality of output voltages of different values are obtained from voltage which is generated in a secondary winding of a transformer through on-off operation of a switching element, characterized in that: a first output voltage is obtained from a flyback voltage which is generated in the whole of said secondary winding when said switching element is in off state, and a second output voltage higher than said first output voltage is obtained from a combination of an induced voltage generated in part of said secondary winding and said first output voltage when said switching element is in on state; and   said first output voltage is stabilized by means of a control system including said switching element and a control circuit connected to a control terminal of said switching element.